Some harder problem for practice in STOICHIOMETRY

1. From the following reaction sequence,
CaC₂ + H₂O ® CaO + C₂H₂
C₂H₂ + H₂ ® C₂H₄
nC₂H₄ ® (C₂H₄)_n
Calculate the mass of polyetheylene which can be produced from 10 kg of CaC₂ Ans. 4375g

2. From the following series of reactions,
Cl₂ + 2KOH ® KCl + KClO + H₂O
3KClO ® 2KCl + KClO₃
4KClO₃ ® 3KClO₄ + KCl
Calculate the mass of chlorine needed to produce 100 g of KClO₄. Ans. 204.5 g

3. Crude calcium carbide is made in an electric furnace by the following reaction :
CaO + 3C ® CaC₂ + CO
The product contains 85% of CaC₂ and 15% of unreacted CaO.
(a) How much CaO is to be added to the furnace charge for each 1000 kg of CaC2 (pure) produced?
(b) How much CaO is to be added to the furnace charge for each 1000 kg of crude product ?
Ans. (a) 1041.5 kg ; (b) 893.7 kg

4. From the following reactions, 2CoF₂ + F₂ ® 2CoF₃
(CH₂)_n + 4n CoF₃ ® (CF₂)n + 2nHF + 4n CoF₂
calculate how much F₂ will be consumed to produce 1 kg of (CF₂)_n. Ans. 1.52 kg

5. A mixture containing KClO₃, KHCO₃, K₂CO₃ and KCl was heated, producing CO₂, O₂ and H₂O gases according to the following equations :
2KClO₃(s) ® 2KCl(s) + 3O₂
2KHCO₃(s) ® K₂O(s) + H₂O(g) + 2CO₂(g)
K₂CO₃(s) ® K₂O(s) + CO₂(g)
The KCl does not react under the conditions of the reaction. If 100.0 g of the mixture produces 1.80 g of H₂O, 13.20 g of CO2 and 4.0 g of O₂, what was the composition of the original mixture ? Ans. (KClO₃ : 10.2 g, KHCO₃ : 20g, K₂CO₃ : 13.8 g

6. A natural gas sample contains 84% (by volume) of CH₄, 10% of of C₂H₆ , 3% of C₃H₈ and 3% of N₂. If a series of catalytic reactions could be used for converting all the carbon atoms of the gas into butadiene, C₄H₆, with 100% efficiency, how much butadiene could be prepared from 100 g of the natural gas ? Ans. 82 g

Thermodynamics

Question-1 True or false?

(a) On the Celsius scale, the boiling point of water at standard pressure is 100.00°C.

(b) Doubling the absolute temperature of an ideal gas at fixed volume and amount of gas will double the pressure.

(c) The ratio PV/mT is the same for all gases in the limit of zero pressure.

(d) The ratio PV/nT is the same for all gases in the limit of zero pressure.

(e) All ideal gases have the same density at 25°C and 1 bar.

(f) All ideal gases have the same number of molecules per unit volume at 25°C and 10 bar.

1. Solutions

(a) True: at standard pressure, the Celsius scale uses 100°C as a reference point.

(b) True: the pressure of an ideal gas is directly proportional to its temperature.

(c) False: Avogadro's hypothesis refers to the number of molecules or atoms of a given

volume. Two equal volumes under the same conditions need not have the same mass (m)

even though they have the same number of molecules.

(d) True: see (c) (e) False: see (c) (f) True: see (c)

Photochemical smog

Photochemical smog

· Smog is a mixture of smoke and fog.

· Oxides of nitrogen and hydrocarbons are let into the atmosphere from automobile

exhaust. The action of sunlight on these pollutants leads to the formation of

peroxyacyl nitrate which causes photochemical smog.

1. Identify electrophiles from the followings.

A. SO₂ B. CH₃OH C. CF₃COOOH D. Pyridine.

2. Identify nucleophiles from the followings.

A. SO₃ B. SO₂Cl₂ C. H₂O D. POCl_3..

3. Which one of the followings is strongest nucleophiles in SN² in proteic solvents.

A. CH₃S^- B. I^- C.H₂O D F^-

4. Which one of the followings is strongest nucleophiles in SN² in proteic solvents.

A. I^- B. Br^- C. Cl^- D. F^-

5. Which one of the followings is strongest nucleophiles in SN² in proteic solvents.

A. OH^- B. ArO^- C. CH₃COO^- D. H₂O

6. Which one of the followings is strongest nucleophiles in SN² in proteic solvents.

A. NH₃ B. NH₂^- C. LDA D. DBU.

7. Which one of the followings is strongest nucleophiles in SN² in proteic solvents.

A. NH₃ B. CH₃NH₂ C. (CH₃)₂NH D.(CH₃)₃N

8. Which one of the followings is strongest nucleophiles in SN² in Aproteic solvents.

A. I^- B. Br^- C. Cl^- D. F^-

9. Identify electrophiles from the followings.

A. CH₄ B. H₂0 C. HOCl D. CH₃MgBr

10. Identify electrophiles from the followings.

A. CCl₄ B. P(Ph)₃ C. C₆H₆ D. CH₃COCl

ans. 1. C 2 C 3 A 4 A 5 A 6 B 7 B 8 D 9 C 10. B

10 objectives in organic mechanism.

1. Identify electrophiles from the followings.

A. SO₂ B. CH₃OH C. CF₃COOOH D. Pyridine.

2. Identify nucleophiles from the followings.

A. SO₃ B. SO₂Cl₂ C. H₂O D. POCl_3..

3. Which one of the followings is strongest nucleophiles in SN² in proteic solvents.

A. CH₃S^- B. I^- C.H₂O D F^-

4. Which one of the followings is strongest nucleophiles in SN² in proteic solvents.

A. I^- B. Br^- C. Cl^- D. F^-

5. Which one of the followings is strongest nucleophiles in SN² in proteic solvents.

A. OH^- B. ArO^- C. CH₃COO^- D. H₂O

6. Which one of the followings is strongest nucleophiles in SN² in proteic solvents.

A. NH₃ B. NH₂^- C. LDA D. DBU.

7. Which one of the followings is strongest nucleophiles in SN² in proteic solvents.

A. NH₃ B. CH₃NH₂ C. (CH₃)₂NH D.(CH₃)₃N

8. Which one of the followings is strongest nucleophiles in SN² in Aproteic solvents.

A. I^- B. Br^- C. Cl^- D. F^-

9. Identify electrophiles from the followings.

A. CH₄ B. H₂0 C. HOCl D. CH₃MgBr

10. Identify electrophiles from the followings.

A. CCl₄ B. P(Ph)₃ C. C₆H₆ D. CH₃COCl

ans. 1. C 2 C 3 A 4 A 5 A 6 B 7 B 8 D 9 C 10. B

Contact-- sinha@kotatimes.com

10 objectives in inorganic chemistry

1. Dimethyl glyoxime forms a square planar complex with Ni²⁺. This complex should be

a.diamagnetic b.paramagnetic having 1 unpaired electron

c.paramagnetic having 2 unpaired electrons d.ferromagnetic.

2.The least stable metal carbonyl as per the bonding considerations should be

a.Cr(CO)₆ b.Mn(CO)₆ c.Fe(CO)₅ d.Ni(CO)₄

3.Platinum metal (Pt) dissolves in aqua-regia but not in concentrated HCl or HNO₃ because

a.HCl oxidizes Pt in the presence of HNO₃

b.HNO₃ reacts with HCl to form chlorine which attacks Pt

c.HNO₃ oxidizes Pt which is followed by formation of a chloro complex

d.HCl and HNO₃ together give O₂ that oxidizes Pt
4.A coordination complex of type MX₂Y₂ [M = metal ion; X,Y = monodentate ligands], can have either a tetrahedral or a square planar geometry. The maximum number of possible isomers in these two cases are respectively a.1 and 2 b.2 and 1 c.1 and 3 d.3 and 2

5..When H₂S is passed through a solution containing Cu²⁺, Cd²⁺ and an excess of cyanide ions, cadmium sulphide precipitates while copper ions remain in solution. This is because

a.Cu²⁺ forms a stable complex with cyanide while Cd²⁺ does not

b.Cu²⁺ forms a more stable complex with cyanide than Cd²⁺

c.Cu²⁺ does not form a sulphide

d.both CdS and CuS are formed, but CuS is soluble

6.Milk of magnesia used as a medicine for treating indigestion is a substance that

a.helps in disintegration of food products leading to their facile metabolism

b.combines with gastric hydrochloric acid thereby enhancing the latter’s efficiency

c.improves the enzymatic activities inside the stomach

d.neutralizes excess acidity, providing a buffered medium inside the stomach

7.In nature, ammonia is synthesized by nitrifying bacteria using enzymes while in industry it is manufactured from N₂ and H₂ using iron oxide catalyst at 550⁰C. Under the same industrial conditions, enzymes cannot be used because

a.enzymes get deactivated at high temperature

b.enzymes catalyze reactions only in living systems

c.the reaction becomes vigorous and uncontrollable

d.the enzymes use nitrates in place of N₂

8.The molar conductivities of H⁺, Li⁺ and Na⁺ ions in aqueous solutions at infinite dilution are in the order

a.H⁺ > Li⁺ > Na⁺ b.H⁺ <>+ <>+ c.H⁺ > Na⁺ > Li⁺ d.Na⁺ > H⁺ > Li⁺

9..Aluminium oxide exists in nature as gems with different colours. The reason for the difference in colour is that

a.the oxidation states of aluminium in these gems are different

b.the extent of crystallinity in these gems is different

c.the Al-O bonding is different in these gem structures

d.there are different transition metal ions present as impurities in these gems

10.There is a mixture of Cu (II) chloride and Fe(II) sulphate. The best way to separate the metal ions from this mixture in qualitative analysis is by treating it with

a.hydrogen sulphide in mild acidic medium, where only Cu (II) sulphide will be precipitated

b.ammonium hydroxide buffer, where only Fe(II) hydroxide will be precipitated

c.hydrogen sulphide in mild acidic medium, where only Fe(II) sulphide will be precipitated

d.ammonium hydroxide buffer, where only Cu (II) hydroxide will be precipitated